Screw-type impeller pumps have been around for some time. These pumps are known for being quite efficient. In such a pump, a screw-shaped impeller is used to pump fluid through a conical suction piece and then into a more conventional pump casing. The idea of a screw-type pump is to pass chunks of solids through the pump, rather than chop up the solids. It is a special case of a “non-clog” pump.
However, binding of the impeller due to fibrous material (e.g., hair, strings, vines, clothing, etc.) winding about the impeller shaft is a significant problem. Binding increases the torque required from the drive motor, and this can lead to motor overloads and nuisance motor overload tripping. That is, during binding the motor power increases causing the motor protection controls to trip the motor offline. When the motor goes offline, the pumping stops and operator intervention is required to place the motor back online. The down-time, of course, detracts from the cost effectiveness of the process.
In some known prior art screw-type centrifugal pumps, the binding issue may be addressed behind the screw-centrifugal impeller by cutting a spiral groove into the backplate. The backplate is typically formed from gray cast iron or ductile iron. These types of iron are not very hard or wear resistant, so the backplate groove may not last very long. Also, a flat plate on the back of the impeller cutting against a spiral groove is not a very efficient cutter, making such a design still highly susceptible to binding problems.
It is therefore desirable to provide a cutter assembly which helps maintain a clear pump area, reduces wear on parts and improves pumping efficiency to reduce motor power load and pump down-time. The disclosed device affords these and other structural, manufacture and operating efficiencies not seen in prior art devices.